Dedicated exhaust gas recirculation engines route the exhaust of a dedicated cylinder(s) back to the air intake where the recirculated exhaust gas is re-introduced into the combustion chambers of the non-dedicated and, optionally, dedicated cylinders. The dedicated exhaust cylinders may operate at a wider range of air to fuel ratios than the remaining cylinders (non-dedicated recirculation cylinders), and fuel to air equivalence ratios, ϕ, of greater than 1, as the recirculated exhaust gas is not directly exhausted from the engine. Often dedicated exhaust gas cylinders are run rich to produce hydrogen and carbon monoxide, whereas the remaining cylinders are often operated near stoichiometric ratio or lean. The addition of the hydrogen and carbon monoxide from the recirculated exhaust gas enhances flame speed, combustion, and knock tolerance of all of the cylinders. Operating the non-dedicated cylinders at or near a fuel to air equivalence ratio, ϕ, of 1.0 or less allows nearly stoichiometric exhaust to leave the engine and a three-way catalyst may be used to reduce pollutant emission. While the complexity and control of reciprocating piston engines including one or more dedicated exhaust gas cylinders is relatively low, there is also relatively little flexibility in operation of dedicated exhaust gas recirculation engines.
Exhaust gas recirculation configurations that utilize high-pressure or low-pressure exhaust gas loops and collect exhaust gas from all of the combustion cylinders, generally lead to a steady supply of exhaust gas in the recirculation loop. In a dedicated exhaust gas recirculation system, however, exhaust gas of a dedicated exhaust gas cylinder is generated once an engine cycle. For example, in the case of an inline, four cylinder engine, flow from a dedicated exhaust gas recirculation cylinder is developed only once every four firing events (i.e., every other crankshaft rotation). This creates a recirculated exhaust gas pulse that may reduce combustion stability and generate cylinder-to-cylinder indicated mean effective pressure imbalances because not all of the cylinders induct the same amount of recirculated exhaust gas as they induct the gas at different times relative to the pulse. An exhaust gas recirculation mixer may mitigate some of the effects of the recirculated exhaust gas pulse spatially and temporally through a number of combustion events. However, it is desirable to provide a dedicated exhaust gas recirculation engine that exhibits relatively more uniform recirculated exhaust gas flow unassisted by an exhaust gas recirculation mixer.